1. Field of the Invention
The present invention relates to rolling bearings and, in particular, to a rolling bearing used in equipment used in vacuum, or equipment which is difficult to be lubricated with oil and grease, such as office automation equipment, information equipment, or the like.
2. Description of the Prior Art
In the prior art, a self-lubricating rolling bearing has been used as a rolling bearing in an environment not suitable for lubrication with oil or grease. In this rolling bearing, a lubricating material is used which does not generate a volatile substance which contaminates the environment. For example, an outer race, an inner race, and rolling members of the rolling bearing are covered with a coating of molybdenum disulfide (Mo S.sub.2). Furthermore, it has been proposed to form a silver film or a lead film on a rolling contact surface (Japanese Utility Model Laid-Open Publication No 58-99521), or to apply a plating of a lubrication metal, such as gold, silver or the like on a surface of rolling members (Japanese Patent Laid-Open Publication No. 5142847).
With regard to a retainer used in such bearings, it has been formed of a resin composite material which contains polytetrafluoroethylene (PTFE) mixed with glass fiber (GF) or molybdenum disulfide (Mo S.sub.2). Alternatively, the retainer has been formed by machining a sinter material containing tungsten disulfide (W S.sub.2), and Mo S.sub.2, mixed with a metal, such as copper (Cu), tin (Sn), tantalum (Ta), and the like.
However, a rolling bearing which exhibits satisfactory lubricating properties under any conditions and which has a long life cannot be achieved only by coating the surface or contact surface of the rolling members with a material having good lubricating properties, such as Mo S.sub.2, gold, silver, lead, or the like, or only by mixing a material of good lubricating properties with the material of the retainer In particular, in a situation in which the self-lubricating properties are required as mentioned above, in order to meet the requirements for wear resistance, low torque, and the like, it is indispensable to take into consideration a relationship between the retainer and the rolling members in which a sliding movement is involved in their operation. Because, in a slide contact, torque is larger than in a rolling contact, and a coated lubricating film is apt to be peeled off.
Furthermore, even if a material having self-lubricating properties is utilized for the retainer, an increase in cost will be encountered if a complicated shape of the retainer is to be formed by machining. Moreover, it is difficult to machine the retainer into a shape which allows the retainer to satisfactorily embrace the rolling members, and problems will arise in which the torque is increased or the assembling becomes inconvenient.